Ring Buffer Functions (rb_xxx)

Classes
struct	RING_BUFFER

Macros
#define	MAX_RING_BUFFER   100

Functions
int	rb_set_nonblocking ()
int	rb_create (int size, int max_event_size, int *handle)
int	rb_delete (int handle)
int	rb_get_wp (int handle, void **p, int millisec)
int	rb_increment_wp (int handle, int size)
int	rb_get_rp (int handle, void **p, int millisec)
int	rb_increment_rp (int handle, int size)
int	rb_get_buffer_level (int handle, int *n_bytes)

Variables
static RING_BUFFER	rb [MAX_RING_BUFFER]
static volatile int	_rb_nonblocking = 0

Detailed Description

dox dox

Macro Definition Documentation

MAX_RING_BUFFER

#define MAX_RING_BUFFER   100

Definition at line 17333 of file midas.cxx.

Function Documentation

rb_create()

int rb_create	(	int	size,
		int	max_event_size,
		int *	handle
	)

Create a ring buffer with a given size

Provide an inter-thread buffer scheme for handling front-end events. This code allows concurrent data acquisition, calibration and network transfer on a multi-CPU machine. One thread reads out the data, passes it via the ring buffer functions to another thread running on the other CPU, which can then calibrate and/or send the data over the network.

Parameters

size	Size of ring buffer, must be larger than 2*max_event_size
max_event_size	Maximum event size to be placed into
*handle	Handle to ring buffer

Returns

DB_SUCCESS, DB_NO_MEMORY, DB_INVALID_PARAM

Definition at line 17389 of file midas.cxx.

{
   int i;
 
   for (i = 0; i < MAX_RING_BUFFER; i++)
      if (rb[i].buffer == NULL)
         break;
 
   if (i == MAX_RING_BUFFER)
      return DB_NO_MEMORY;
 
   if (size < max_event_size * 2)
      return DB_INVALID_PARAM;
 
   memset(&rb[i], 0, sizeof(RING_BUFFER));
   rb[i].buffer = (unsigned char *) M_MALLOC(size);
   assert(rb[i].buffer);
   rb[i].size = size;
   rb[i].max_event_size = max_event_size;
   rb[i].rp = rb[i].buffer;
   rb[i].wp = rb[i].buffer;
   rb[i].ep = rb[i].buffer;
 
   *handle = i + 1;
 
   return DB_SUCCESS;
}

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rb_delete()

int rb_delete

(

int

handle

)

Delete a ring buffer

Parameters

handle

Handle of the ring buffer

Returns

DB_SUCCESS

Definition at line 17443 of file midas.cxx.

{
   if (handle < 0 || handle >= MAX_RING_BUFFER || rb[handle - 1].buffer == NULL)
      return DB_INVALID_HANDLE;
 
   M_FREE(rb[handle - 1].buffer);
   rb[handle - 1].buffer = NULL;
   memset(&rb[handle - 1], 0, sizeof(RING_BUFFER));
 
   return DB_SUCCESS;
}

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rb_get_buffer_level()

int rb_get_buffer_level	(	int	handle,
		int *	n_bytes
	)

Return number of bytes in a ring buffer

Parameters

handle	Handle of the buffer to get the info
*n_bytes	Number of bytes in buffer

Returns

DB_SUCCESS, DB_INVALID_HANDLE

Definition at line 17738 of file midas.cxx.

{
   int h;
 
   if (handle < 1 || handle > MAX_RING_BUFFER || rb[handle - 1].buffer == NULL)
      return DB_INVALID_HANDLE;
 
   h = handle - 1;
 
   if (rb[h].wp >= rb[h].rp)
      *n_bytes = (POINTER_T) rb[h].wp - (POINTER_T) rb[h].rp;
   else
      *n_bytes =
              (POINTER_T) rb[h].ep - (POINTER_T) rb[h].rp + (POINTER_T) rb[h].wp - (POINTER_T) rb[h].buffer;
 
   return DB_SUCCESS;
}

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rb_get_rp()

int rb_get_rp	(	int	handle,
		void **	p,
		int	millisec
	)

Obtain the current read pointer at which new data is available with optional timeout

Parameters

handle	Ring buffer handle
millisec	Optional timeout in milliseconds if buffer is full. Zero to not wait at all (non-blocking)
**p	Address of pointer pointing to newly available data. If p == NULL, only return status.

Returns

DB_SUCCESS, DB_TIEMOUT, DB_INVALID_HANDLE

Definition at line 17621 of file midas.cxx.

{
   int i, h;
 
   if (handle < 1 || handle > MAX_RING_BUFFER || rb[handle - 1].buffer == NULL)
      return DB_INVALID_HANDLE;
 
   h = handle - 1;
 
   for (i = 0; i <= millisec / 10; i++) {
 
      if (rb[h].wp != rb[h].rp) {
         if (p != NULL)
            *p = rb[handle - 1].rp;
         return DB_SUCCESS;
      }
 
      if (millisec == 0)
         return DB_TIMEOUT;
 
      if (_rb_nonblocking)
         return DB_TIMEOUT;
 
      /* wait one time slice */
      ss_sleep(10);
   }
 
   return DB_TIMEOUT;
}

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rb_get_wp()

int rb_get_wp	(	int	handle,
		void **	p,
		int	millisec
	)

Retrieve write pointer where new data can be written

Parameters

handle	Ring buffer handle
millisec	Optional timeout in milliseconds if buffer is full. Zero to not wait at all (non-blocking)
**p	Write pointer

Returns

DB_SUCCESS, DB_TIMEOUT, DB_INVALID_HANDLE

Definition at line 17480 of file midas.cxx.

{
   int h, i;
   unsigned char *rp;
 
   if (handle < 1 || handle > MAX_RING_BUFFER || rb[handle - 1].buffer == NULL)
      return DB_INVALID_HANDLE;
 
   h = handle - 1;
 
   for (i = 0; i <= millisec / 10; i++) {
 
      rp = rb[h].rp;            // keep local copy for convenience
 
      /* check if enough size for wp >= rp without wrap-around */
      if (rb[h].wp >= rp
          && rb[h].wp + rb[h].max_event_size <= rb[h].buffer + rb[h].size - rb[h].max_event_size) {
         *p = rb[h].wp;
         return DB_SUCCESS;
      }
 
      /* check if enough size for wp >= rp with wrap-around */
      if (rb[h].wp >= rp && rb[h].wp + rb[h].max_event_size > rb[h].buffer + rb[h].size - rb[h].max_event_size &&
          rp > rb[h].buffer) {    // next increment of wp wraps around, so need space at beginning
         *p = rb[h].wp;
         return DB_SUCCESS;
      }
 
      /* check if enough size for wp < rp */
      if (rb[h].wp < rp && rb[h].wp + rb[h].max_event_size < rp) {
         *p = rb[h].wp;
         return DB_SUCCESS;
      }
 
      if (millisec == 0)
         return DB_TIMEOUT;
 
      if (_rb_nonblocking)
         return DB_TIMEOUT;
 
      /* wait one time slice */
      ss_sleep(10);
   }
 
   return DB_TIMEOUT;
}

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rb_increment_rp()

int rb_increment_rp	(	int	handle,
		int	size
	)

Increment current read pointer, freeing up space for the writing thread.

Parameters

handle	Ring buffer handle
size	Number of bytes to free up at current read pointer

Returns

DB_SUCCESS, DB_INVALID_PARAM

Definition at line 17683 of file midas.cxx.

{
   int h;
 
   unsigned char *new_rp;
   unsigned char *ep;
 
   if (handle < 1 || handle > MAX_RING_BUFFER || rb[handle - 1].buffer == NULL)
      return DB_INVALID_HANDLE;
 
   h = handle - 1;
 
   if ((DWORD) size > rb[h].max_event_size)
      return DB_INVALID_PARAM;
 
   new_rp = rb[h].rp + size;
   ep = rb[h].ep; // keep local copy of end pointer, rb[h].ep might be changed by other thread
 
   /* wrap around if end pointer reached */
   if (new_rp >= ep && rb[h].wp < ep)
      new_rp = rb[h].buffer;
 
   rb[handle - 1].rp = new_rp;
 
   return DB_SUCCESS;
}

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rb_increment_wp()

int rb_increment_wp	(	int	handle,
		int	size
	)

rb_increment_wp

Increment current write pointer, making the data at the write pointer available to the receiving thread

Parameters

handle	Ring buffer handle
size	Number of bytes placed at the WP

Returns

DB_SUCCESS, DB_INVALID_PARAM, DB_INVALID_HANDLE

Definition at line 17555 of file midas.cxx.

{
   int h;
   unsigned char *new_wp;
 
   if (handle < 1 || handle > MAX_RING_BUFFER || rb[handle - 1].buffer == NULL)
      return DB_INVALID_HANDLE;
 
   h = handle - 1;
 
   if ((DWORD) size > rb[h].max_event_size) {
      cm_msg(MERROR, "rb_increment_wp", "event size of %d MB larger than max_event_size of %d MB",
             size/1024/1024, rb[h].max_event_size/1024/1024);
      abort();
   }
 
   new_wp = rb[h].wp + size;
 
   /* wrap around wp if not enough space */
   if (new_wp > rb[h].buffer + rb[h].size - rb[h].max_event_size) {
      rb[h].ep = new_wp;
      new_wp = rb[h].buffer;
      assert(rb[h].rp != rb[h].buffer);
   } else
      if (new_wp > rb[h].ep)
         rb[h].ep = new_wp;
 
   rb[h].wp = new_wp;
 
   return DB_SUCCESS;
}

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rb_set_nonblocking()

int rb_set_nonblocking

(

void

)

dox Set all rb_get_xx to nonblocking. Needed in multi-thread environments for stopping all theads without deadlock

Returns

DB_SUCCESS

Definition at line 17348 of file midas.cxx.

{
   _rb_nonblocking = 1;
 
   return DB_SUCCESS;
}

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Variable Documentation

_rb_nonblocking

volatile int _rb_nonblocking = 0

static

Definition at line 17337 of file midas.cxx.

rb

RING_BUFFER rb[MAX_RING_BUFFER]

static

Definition at line 17335 of file midas.cxx.